Received April 20, 2009; Revision received June 8, 2009
Addition of chitosan or H2O2 caused destruction of
nuclei of epidermal cells (EC) in the epidermis isolated from pea
leaves. Phenol, a substrate of the apoplastic peroxidase-oxidase, in
concentrations of 10–10-10–6 M
prevented the destructive effect of chitosan. Phenolic compounds
2,4-dichlorophenol, catechol, and salicylic acid, phenolic uncouplers
of oxidative phosphorylation pentachlorophenol and 2,4-dinitrophenol,
and a non-phenolic uncoupler carbonyl cyanide
m-chlorophenylhydrazone, but not tyrosine or guaiacol, displayed
similar protective effects. A further increase in concentrations of the
phenolic compounds abolished their protective effects against chitosan.
Malate, a substrate of the apoplastic malate dehydrogenase, replenished
the pool of apoplastic NADH that is a substrate of peroxidase-oxidase,
prevented the chitosan-induced destruction of the EC nuclei, and
removed the deleterious effect of the increased concentration of phenol
(0.1 mM). Methylene Blue, benzoquinone, and
N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD)
capable of supporting the optimal catalytic action of
peroxidase-oxidase cancelled the destructive effect of chitosan on the
EC nuclei. The NADH-oxidizing combination of TMPD with ferricyanide
promoted the chitosan-induced destruction of the nuclei. The data
suggest that the apoplastic peroxidase-oxidase is involved in the
antioxidant protection of EC against chitosan and
H2O2.
KEY WORDS: apoplastic peroxidase, programmed cell death,
chitosan, hydrogen peroxide, phenolic compounds, protective action,
plants, epidermal cells